There has been proposed a technology of wiring in a multi-layered structure as an approach for a high integration of a semiconductor device. In order to obtain the multi-layered wiring, an nth layer and an (n+1)th layer are connected to each other through a conductive layer while a thin film called as an interlayer insulating film is formed in areas other than the conductive layer. A SiO2 film is widely used as a typical interlayer insulating film. To further accelerate the speed of an operation of the semiconductor device, it is required to lower the dielectric constant of the interlayer insulating film and to this end, much attention has been paid recently on a fluorine-containing carbon film (fluorocarbon film) which is a compound of carbon C and fluorine F. Whereas the relative dielectric constant of the SiO2 film is about 4, that of the fluorine-containing carbon becomes, e.g., 2.5 or less by appropriately selecting a source gas so that it is very useful as the interlayer insulating film.
There is disclosed in Japanese Patent Laid-open Publication No. 10-44667 a technology of forming a fluorine-containing carbon film on a semiconductor wafer (hereinafter, referred to as “wafer”) by using an electron cyclotron resonance (“ECR”) plasma processing apparatus. Specifically, a microwave and a magnetic field interact with each other to cause ECR, so that a plasma generating gas such as Ar gas is converted into a plasma and a source gas such as C5F8 gas is then activated by the plasma to form the fluorine-containing carbon film on the wafer. In this technology, however, the fluorine-containing carbon film is deposited on the inner surface of a processing chamber and around a mounting table while the film forming process for the wafer is repeated, and the accumulation of the deposits grows to make it thick enough to be detached therefrom, thereby producing particles. Accordingly, after the film forming process is repeated a predetermined number of times (e.g., 12 times), the inside of the processing chamber is cleaned by using an oxygen plasma and the inner wall thereof is then coated with a thin precoat film of fluorine-containing carbon.
However, the fluorine-containing carbon film formed by using the ECR plasma processing apparatus has a high leakage current and is very brittle, so that adhesivity thereof is poor. To that end, it is impossible to obtain a fluorine-containing carbon film having a quality good enough to be used in an actual device with the ECR plasma processing apparatus.
Accordingly, the inventors have researched and developed a plasma processing apparatus as shown in FIG. 5. The apparatus includes a processing chamber 81 in which a mounting table 85 is provided, and a disc-shaped planar antenna member 8 disposed at an upper portion of the processing chamber 81 to face the mounting table 85. The planar antenna member 8 has a plurality of slots circumferentially formed therein to emit a microwave therethrough. Disposed under the planar antenna member 8 is a dielectric plate 80 for transmitting the microwave radiated from the planar antenna member 8 therethrough. Further, a gas supply member (shower head) 83 made of aluminum is provided between the dielectric plate 80 and the mounting table 85. The gas supply member 83 divides the inside of the processing chamber 81 into an upper plasma generation space 82 and a lower processing space 86. Moreover, the gas supply member 83 has a plurality of through-holes 84 through which the spaces 82, 86 communicate with each other and a plurality of gas supply openings (not shown) opened in the bottom surface thereof.
In this apparatus, Ar gas introduced into the plasma generation space 82 is activated by the microwave radiated from the planar antenna member 8 through the dielectric plate 80. Further, C5F8 gas supplied through the gas supply openings in the shower head 83 flows into the plasma generation space 82 to diffuse therein and is activated by the Ar plasma. The active species of CF compound thus generated flow down into the processing space 86 through the through-holes 84 to be deposited onto the surface of the wafer W on the mounting table 85, thereby forming a fluorine-containing carbon film. Thus obtained fluorine-containing carbon film has a low leakage current and a good adhesivity.
It is conjectured that the improvement achieved in film quality as described above is realized because the plasma density is higher and the electron temperature is lower in the apparatus shown in FIG. 5 than in the ECR plasma processing apparatus. Meanwhile, if a fluorine-containing carbon film is attached to the bottom surface of the dielectric plate 80, a part of the microwave is absorbed by the fluorine-containing carbon film. Further, the nonuniform thickness of the fluorine-containing carbon film attached to the bottom surface of the dielectric plate 80 makes the transmittance of the microwave nonuniform, which deteriorates the uniformity of the generated plasma to adversely influence the film forming process on the wafer. The degree of the influence depends on the thickness of the film attached to the dielectric plate 80 and a target thickness of the film formed on the wafer. However, in view of making the interlayer insulating film thinner, the presence of the attached film itself becomes problematic. Furthermore, in case of processing a plurality of wafers sequentially, the thickness of the film attached to the bottom surface of the dielectric plate 80 gradually varies, thereby resulting in differences in thickness of the fluorine-containing carbon films formed on the surfaces of the respective wafers.
Further, in the apparatus shown in FIG. 5, as a material of the shower head 83, an aluminum member of great corrosion-resistance is used. On the surface of the shower head 83 made of aluminum, there occurs a bond of aluminum and fluorine by the plasma of the C5F8 gas which is a CF-based gas, thus forming a passivation film. However, if the surface of the shower head 83 is exposed to oxygen plasma during a cleaning process, the passivation film is decomposed to expose the aluminum. In addition, since the shower head 83 faces the planar antenna member 8 via the plasma generation space 82, it undergoes the sputtering action due to Ar ions while the film forming process is performed on the wafer. Accordingly, the wafer may be contaminated by the scattering of aluminum.